The present invention relates to a device using a piezoelectric/electrostrictive film, particularly to the structure of a piezoelectric/electrostrictive device for improving the operational characteristic of an element for converting electrical energy into mechanical energy such as mechanical displacement, mechanical force, or vibration and etc., and vice versa. Specifically, the present invention relates to a piezoelectric/electrostrictive device to be applied to transducers, various actuators, frequency-region functional components (filters), transformers, vibrators and resonators for communication and motive power, oscillators, discriminators, and various sensors including ultrasonic sensors, acceleration sensors, angular velocity sensors, impact sensors, and mass sensors, and moreover unimorph- and bimorph-type elements used for servo shift elements described in xe2x80x9cFrom Foundation Up To Application of Piezoelectric/Electrostrictive Actuatorxe2x80x9d written by Kenji Uchino {edited by Japan Industrial Technical Center and published by MORIKITA SHUPPAN (transliterated)}, and to be preferably adopted to various actuators used for mechanisms for shift and positioning adjustment and angle adjustment of various precision components and etc. of optical equipment, precision equipment, etc.
Recently, a shift control element for adjusting an optical-path length or position on the sub-micron order has been requested in the optical and magnetic recording fields, as well as the precision-machining field. To respond to this request, piezoelectric/electrostrictive actuators have been developed, which are elements using a displacement based on the reverse or converse piezoelectric effect or electrostrictive effect caused by applying an electric field to a piezoelectric/electrostrictive material such as a ferroelectric.
In the field of magnetic recording on a hard disc drive, storage capacity has been remarkably increased in recent years. This is because an attempt has been made to use a recording medium more efficiently by increasing the number of recording tracks to increase the recording density. Recording methods have also improved.
This attempt has been mainly made so far in the area of the voice coil motor. Moreover, as a new technical art, an electrostatic-type microactuator micromachined in Si or Ni and used as the tracking system of a magnetic head for a hard-disk drive has been attempted, as described on pp. 1081-1084 in the preliminary manuscript collection of xe2x80x9c1997 International Conference on solid-state Sensors and Actuatorsxe2x80x9d of xe2x80x9cTRANSDUCER""97xe2x80x9d.
Moreover, Japanese Patent Application Laid-Open No. 10-136665 discloses a piezoelectric actuator as shown in FIG. 24 in which a fixed portion 103, a movable portion 104, and at least one beam portion 102 for connecting the portions 103 and 104 to each other are integrally formed by forming at least one hole on a flat body made of a piezoelectric/electrostrictive material, and a strain generation portion is constituted by forming an electrode layer 105 on at least a part of at least one beam portion 102 so that an expansion or a contraction motion occurs in the direction connecting the fixed portion 103 with the movable portion 104, and a displacement mode of the movable portion 104 to the fixed portion 103 generated due to the expansion or contraction motion of the strain generation portion is an arc-shaped or rotational mode in the plane of the flat body.
However, in the case of the conventional art for positioning a recording head mainly using a voice coil motor, it is difficult to accurately position a recording head so as to accurately trace tracks when the number of tracks increases in order to correspond to a further increase in capacity.
The above-described technical art using an electrostatic-type microactuator obtains a displacement by applying a voltage between a plurality of flat electrodes formed through micromachining. However, it is difficult to increase a resonance frequency because of the structure. Consequently, the technical art includes such problems that vibrations are not easily attenuated when a high-speed operation is performed. Moreover, there is a feature that the technical art is displacement-theoretically inferior in the linearity of the voltage-displacement characteristic. Therefore, there are many problems to be solved from the viewpoint of accurate alignment. Furthermore, the process of micromachining itself has a problem from the viewpoint of the manufacturing cost.
Furthermore, in the case of a piezoelectric actuator disclosed in Japanese Patent Application Laid-Open No. 10-136665, the piezoelectric-operation portion has a monomorph structure. Therefore, the main-strain axis of a piezoelectric material becomes coaxial or parallel with the main-shift axis of the piezoelectric-operation portion. Thus, there are problems that the piezoelectric-operation portion itself generates only a small shift and the movable portion also shows a small displacement. Moreover, the piezoelectric actuator itself is heavy and subject to harmful vibrations for operation such as residual vibrations and vibrational noises under a high-speed operation as described in Japanese Patent Application Laid-Open No. 10-136665 and therefore, it is necessary to suppress harmful vibrations by injecting a filler into a hole. However, the use of such a filler may adversely influence displacement of the movable portion. Moreover, because it is unavoidable to constitute a piezoelectric actuator with a piezoelectric/electrostrictive material inferior in mechanical strength, there is a problem that the actuator is subject to material strength-imposed restrictions on shape and purpose.
The present invention is made to solve the problems of the above piezoelectric/electrostrictive device. According to the present invention, the following first to sixth piezoelectric/electrostrictive devices capable of accurately performing in-plane movements and operations at a high speed are provided.
That is, a piezoelectric/electrostrictive device in which a piezoelectric element is formed on at least a portion of at least one plane of a diaphragm whose one side is joined to a substrate and at least one side of one thin-walled fixing plate is joined to one side of the diaphragm so that the plane of the fixing plate and the plane of the diaphragm are perpendicularly intersected with each other, is provided as the first piezoelectric/electrostrictive device.
It is preferable that the first piezoelectric/electrostrictive device operates in accordance with at least either of a xcex8-mode displacement in which a fixing plate is displaced like a pendulum in the direction vertical to a side of the fixing plate and vertical to the vertical axis about the vertical axis vertically passing through the center of a fixed plane by using the joining face between the fixing plate and a diaphragm as the fixed plane and a xcfx86-mode displacement in which a swing in the direction vertical to a side of the fixing plate and vertical to the vertical axis is displaced like a pendulum while being followed by a swing in the direction parallel with a side of the fixing plate, that is, the first piezoelectric/electrostrictive device drives the fixing plate by a piezoelectric element or detects the displacement amount of the fixing plate.
Moreover, a piezoelectric/electrostrictive device in which a fixing plate and a connection plate are joined with each other at their sides, and a diaphragm in which piezoelectric elements are arranged on at least a portion of at least one plane is joined to the connection plate at their sides in the direction perpendicular to the joining direction between the fixing plate and the connection plate, and at least parts of sides of the connection plate and the diaphragm are joined to a substrate, is provided as the second piezoelectric/electrostrictive device.
In this case, a part of a side of the connection plate to be joined to the substrate represents a side opposite to the connection face of the connection plate with the diaphragm. Therefore, the fixing plate and the substrate are connected with each other through the connection plate. A part of a side of the diaphragm to be joined to the substrate represents a side opposite to the connection face of the diaphragm to the connection plate or a side opposite to the connection face of the diaphragm to the fixing plate when the diaphragm is directly joined to the fixing plate. Moreover, the joining configuration between the connection plate or diaphragm and the substrate is common to piezoelectric/electrostrictive devices of the present invention to be described later.
Furthermore, a piezoelectric/electrostrictive device in which a fixing plate and a connection plate are joined with each other at their sides, and two diaphragms are joined at their sides so as to hold the connection plate in the direction perpendicular to the joining direction between the fixing plate and the connection plate, piezoelectric elements are arranged on at least a portion of at least one plane of at least one diaphragm, and at least parts of sides of the connection plate and each diaphragm are connected with a substrate is provided as the third piezoelectric/electrostrictive device.
In case of the third piezoelectric/electrostrictive device, it is preferable to arrange piezoelectric elements on at least one plane of one diaphragm and one or preferably, a plurality of slits on the other diaphragm. Moreover, in case of the second and third piezoelectric/electrostrictive devices, it is preferable to join other diaphragm plates in which piezoelectric elements are arranged at one end of a fixing plate at their sides and alternately join a necessary number of other connection plates and/or fixing plates and other diaphragms to the above other diaphragms at their sides to increase a displacement amount.
Then, a piezoelectric/electrostrictive device in which a connection plate and a diaphragm in which piezoelectric elements are arranged on at least a portion of at least one plane are not connected with each other but connected with a fixing plate at their sides in parallel and at least parts of the sides of the connection plate and the diaphragm are joined to a substrate is provided as the fourth piezoelectric/electrostrictive device.
Moreover, a piezoelectric/electrostrictive device in which a fixing plate joined to and held by two connection plates at sides is set between lateral sides of a concave portion formed on a substrate so as to be set between the lateral sides, two diaphragms are respectively set between each of the connection plates and the bottom sides of concave portion in the direction perpendicular to the direction for the connection plates to hold the fixing plate, and piezoelectric elements are arranged on at least a portion of at least one plane of at least one diaphragm is provided as the fifth piezoelectric/electrostrictive device. In this case, the concave portion represents a portion comprising facing sides and a bottom side for connecting these sides. In case of the present invention, it is not always necessary that a bottom side is a plane. It is possible to change the bottom side to various shapes by forming a recess or a protrusion on the bottom side as long as it does not influence the displacement of a fixing plate or measurement of a displacement amount.
Moreover, a piezoelectric/electrostrictive device in which a fixing plate is joined to and held by two connection plates at sides is set on a through-hole formed in a substrate, at least a plurality of diaphragms is bridged between each of the connection plate and the through-hole or between the fixing plate and the through-hole so as to span them in the direction perpendicular to the direction for the connection plates to hold the fixing plate, and piezoelectric elements are arranged on at least a portion of at least one plane of at least one of the diaphragm is provided as the sixth piezoelectric/electrostrictive device.
In case of the sixth piezoelectric/electrostrictive device, it is preferable to arrange piezoelectric elements on at least one plane of one diaphragm among pairs of diaphragms facing each other through each connection plate or a fixing plate and to form one or preferably, a plurality of slits on the other diaphragm.
In case of the second to sixth piezoelectric/electrostrictive devices, it is preferable to form a slit or constricted portion (narrow portion) on a connection plate because a displacement amount can be increased. Moreover, it is preferable to use a structure in which a diaphragm is fitted to and joined to a concave portion formed by a connection plate and a substrate. To obtain the above structure, it is preferable to integrally form a fixing plate, connection plate, and diaphragm from one diaphragm plate and form a substrate integrally with a diaphragm plate and a base plate by superimposing the diaphragm plate on the base plate. The concave portion represents a concave portion in which a substrate itself is formed into a concave shape, a concave portion in which a cutout is formed on a part of the outer periphery of a substrate, or a concave portion when regarding a part of a through-hole formed on a substrate as a concave portion.
Moreover, it is preferable to bond a spring plate with at least one plane of a connection plate and join the spring plate to a substrate or a spring-plate reinforcement portion. In this case, it is preferable that the spring plate is not bonded by using an adhesive or the like but the spring plate is formed integrally with an intermediate plate fitted between and integrated with a diaphragm plate and a base plate or formed integrally with a spring-plate reinforcement portion formed integrally with the diaphragm plate and also formed integrally with a connection plate. In case of the spring plate, when there are two or more connection plates, it is preferable that shapes formed by bonding connection plates with the spring plate become the same. Moreover, though the shape of the spring plate is not restricted, it is preferable to use a simple shape such as a pillar-shape or plate shape or a shape to be easily formed such as a U-shaped, H-shaped, or quadrangular frame because the manufacturing process can be simplified. Furthermore, it is preferable to use a reinforcement plate to be bonded with a spring plate and joined to a side of a substrate. In this case, it is preferable to form the reinforcement plate integrally with the spring plate and the substrate.
These second to sixth piezoelectric/electrostrictive devices respectively have a structure preferable to use either of a xcex8-mode displacement in which a fixing plate displaces like a pendulum in the direction vertical to a side of the fixing plate and vertical to the vertical axis vertically passing through the center of a fixed plane about the vertical axis by using the joining face between a connection plate and a substrate as the fixed plane and a xcfx86-mode displacement in which a swing in the direction vertical to a side of the diaphragm and vertical to the vertical axis displaces like a pendulum while being followed by a swing in the direction parallel with a side of the fixing plate.
Moreover, in case of every piezoelectric/electrostrictive device described above, it is preferable to form a diaphragm and/or a connection plate by joining the diaphragm and/or connection plate to a side of an optional-shaped through-hole formed in a substrate because the piezoelectric/electrostrictive device can be easily handled and its damage can be avoided. Furthermore, it is preferable to divide one piezoelectric element into two parts and use one of them as a driving element and the other of them as an auxiliary element because it is possible to improve the positioning accuracy. In this case, the auxiliary element represents a trouble-shooting element, displacement confirming/deciding element, or auxiliary driving element. Furthermore, it is preferable to arrange piezoelectric elements on at least two places and use the piezoelectric element on at least one place as a driving element and the piezoelectric element on at least the other place as an auxiliary element because the driving accuracy and positioning accuracy are improved. Therefore, it is also possible to further divide each of piezoelectric elements arranged on two places or more into two parts.
Furthermore, it is preferable to cover each piezoelectric element, the electrode of the piezoelectric element, and an electrode lead to be connected to the electrode with an insulating coating layer made of resin or glass. Thus, even under a state in which a piezoelectric-element portion is soaked in a liquid, the electrode is not short-circuited and it is possible to use the piezoelectric/electrostrictive device. In this case, to improve the performance of the piezoelectric/electrostrictive device, it is preferable to use resin as an insulating coating material instead of glass, fluorocarbon resin superior in chemical stability is most preferably used, and it is also possible to preferably use silicon resin though this is inferior to fluorocarbon resin in chemical stability. When forming the above insulating coating layer, it is preferable to further form a shielding layer made of conductive materials on the surface of the insulating coating layer to minimize the influence of external noises such as electromagnetic waves.
It is preferable that substrate, fixing plate, connection plate, diaphragm, spring plate, spring-plate reinforcement portion, and reinforcement plate constituting a piezoelectric/electrostrictive device of the present invention are integrally formed by using a stabilized or partially-stabilized zirconia. A material mainly containing a component made of lead zirconate, lead titanate, and lead magnesium niobate is preferably used as the piezoelectric film of the piezoelectric element. Moreover, by trimming and adjusting the shape of a fixing plate, spring plate, or connection plate through laser-beam processing or cutting, it is possible to obtain a preferable shape each time depending on the type of an actuator to be applied. Furthermore, it is possible to easily adjust the displacement amount of a fixing plate. Furthermore, it is preferable to adjust the effective electrode area of the piezoelectric element by laser-beam-processing or cutting the electrode of a piezoelectric element, because a piezoelectric characteristic suitable for a use or a necessary spec can be easily obtained.
As the result of comparing a piezoelectric/electrostrictive device of the present invention with the piezoelectric actuator disclosed in Japanese Patent Application Laid-Open No. 10-136665, because the piezoelectric/electrostrictive device of the present invention has a unimorph- or bimorph-type structure having a diaphragm and thereby, the direction of the main-strain axis of a piezoelectric material is different from that of the main-displacement axis of a piezoelectric operating portion (portion causing a displacement by the strain of the piezoelectric material), it is found that the piezoelectric/electrostrictive device of the present invention has advantages that the strain of the piezoelectric material can be enlarged to the bending mode by effectively using the above feature and therefore, a large displacement of a fixing plate can be obtained. Moreover, a piezoelectric/electrostrictive device of the present invention allows functional differentiation and its substrate and the like other than its piezoelectric material can be constituted with a material mainly containing zirconia superior in mechanical strength and toughness. Therefore, there is an advantage that a compact, thin, and lightweight device having a desired strength can be obtained. Furthermore, a piezoelectric/electrostrictive device of the present invention has features that the displacing characteristic is not easily influenced from the outside and therefore, it is unnecessary to use a filler or the like.
The expression xe2x80x9cpiezoelectricxe2x80x9d of piezoelectric element, piezoelectric film, and piezoelectric ceramics used for the present invention includes the meanings of both xe2x80x9cpiezoelectricxe2x80x9d and xe2x80x9celectrostrictive.xe2x80x9d